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Keywords

Fence diagram; fundamental frequency; sediment thickness.

Abstract

The Abbottabad basin is mainly composed of different loose and indurated sediments such as fine to medium grain silt and clay and large to medium sized boulders and cobbles, occupying a low land between the hills. These sediments are primarily stream deposits and variably compacted in the form of rock, suggested name Havelian group after their maximum thickness into Havelian area. Numerous streams converge at the Abbottabad intermontane basin from the north–northeast and join to form a single channel that passes through a narrow gorge on the western side of the Sirban hill. Geomorphically, the Abbottabad city is underlain by a thick sequence of loose Quaternary–Recent alluvial sediments, making it vulnerable to seismic hazards. This research determines the sediment thickness for the Abbottabad basin using a geophysical approach. In this regard, thirteen lithologic profiles were developed in the Abbottabad basin at different locations. These profiles were ultimately combined to develop a Fence diagram showing a generalized stratigraphic pattern of the Quaternary–Recent unconsolidated sediments in the basin. Standard Penetration Test (SPT) and H/V analysis were used to characterize the site and shear wave velocity at a different location of Abbottabad basin and surrounding area. Based on H/V data (using Tromino Engy Plus instrument) Abbottabad basin and immediate surroundings have an average fundamental frequency from 0.5 to 9 Hz, which represents the deposition of alluvial sediments (i.e., stiff and dense soil).